1. Field of the Invention
The invention generally relates to position sensors. A position sensor usually has a zero signal output at the null or zero position which frequently occurs in the middle of its operating range. The disclosed invention specifically relates to an inductive position sensor with a level detector acting as a fault indicator which has the ability to monitor the signal output of the inductive position sensor at every position and to indicate failure when the signal output is below a given minimum signal level.
2. Description of the Prior Art
Many techniques have been developed to aid in determination of whether a position sensor is properly operating. Most of these techniques suffer from disadvantage in that they limit the use of the position sensor or otherwise restrict its field of operation. For example, inductive position sensors normally have a zero signal output in the middle of their operating range, usually the null or zero point. Failure may be detected if the operation is restricted to angles which are greater or less than zero and which will always produce some minimal signal output of the position sensor so that an output signal is always present for monitoring. If operation through the zero position is required, the normal signal at zero is zero and a failure is not distinguishable from normal operation.
U.S. Pat. No. 2,823,877, issued to Hess, is one such example of the prior art wherein it suggests the concept of utilizing the output of phase-sensitive demodulators to create an analog signal which is monitored to detect failure of a servo system. As noted above, this concept suffers from the problem that the zero position results in a zero signal output and failure is not distinguishable from normal operation at this point.
The utilization of an integrated circuit to provide a limited signal applied to a level detector which functions at a fault monitor when the signal rises above a preset limit is also known in the prior art as taught by U.S. Pat. No. 3,778,696 issued to R. G. Walters.